update code to reflect the new minimum python version 3.7

- update string format method
- remove redundant default arguments from function  calls
- remove unused imports
- remove unicode identifier from strings, it's default in py3 (see: https://stackoverflow.com/a/4182635/12201331)

allianceauth/groupmanagement/tests/test_admin.py

@@ -25,7 +25,7 @@ else:
 MODULE_PATH = 'allianceauth.groupmanagement.admin'
 
 
-class MockRequest(object):
+class MockRequest:
 
     def __init__(self, user=None):
         self.user = user